In order to use one-cycle control method in three-phase four-wire power system, this paper partitions the main circuit of three-phase four-wire APF with four-leg into two sub-circuits, including three-phase bridge circuit and N-phase half-bridge circuit which are based on one-cycle control independently. The one-cycle control equation and control circuit in three-phase bridge is similar to the three-phase three-wire system, the control equation and control circuit in N-phase half-bridge is mainly set up through analysis to the circuit. After that, the simulation of overall circuit is used to validate the scheme. The simulation results verify the control circuit is very simple, and can compensate the neutral current as well as three-phase harmonic and reactive currents effectively. So this control method should have a good application in three-phase four-wire systems.